It’s no secret that there will be significant challenges to achieving a clean energy future where a large percentage of society’s energy comes from renewable resources such as solar and wind. Many of these challenges relate to the fact that solar and wind are variable and sometimes intermittent generators– they only produce electricity when the sun is shining and the wind is blowing. Thus, the amount of electricity supplied by these resources is often out of sync with the demand for electricity, an issue that gets worse as solar and wind achieves a larger percentage of a region’s generating capacity. In order to deal with the imbalance with supply and demand, a combination of three actions are often taken:

The price of electricity decreased. Sometimes, electricity prices can even go negative, with a state like CA having excess electricity paying states like Arizona to take the extra electricity off their grid (see article below).

Conventional power plants, such as natural gas plants, are turned off/on to help balance demand and supply.

Excess electricity from solar and/or wind is curtailed, meaning the connection between the solar panel or wind turbine and the grid is cut, and the electricity is wasted. (free electricity!).

In California, where almost 14% of its electricity was obtained from solar in 2016, this grid balancing act is already becoming extremely challenging, as discussed in a recent LA Times article that provides a lot of useful stats and discussion:

In China, which is the world leader in solar panel production and increasingly installing large amounts of solar power plants itself, the imbalance between electricity supply and demand is become especially acute in provinces where transmission of electricity to the large population centers is highly inadequate. According to the article below, curtailment rates of solar-generated electricity are often 30% or higher!:

While improvements to the grid (e.g. smart grid technologies) and demand-side management can go a long way to help alleviate some of the issues involved with balancing electricity supply and demand, there is a limit to how much they can help—especially in a future where solar and wind generate 50% or more of a region’s electricity. In this case, many studies agree that low-cost and scalable energy storage technologies are crucially important. Batteries are one option, and have the benefit of high round trip efficiencies, but electrolyzer technologies that convert electricity into storable chemical fuels are another option. Electricity-to-fuel technologies such as the ones we work on in our lab also represent a huge opportunity because fuels can be used for many energy applications and sectors that are not currently very reliant on electricity. The flexibility and storability of fuels thus make them highly attractive 1.) for their ability to utilize low-cost or free electricity, and 2.) their ability to impact many different energy use sectors (transportation, industrial/chemical, agriculture, commercial) that are predominantly reliant on fossil-fuels at this time.

^credit: the term “The grid’s great balancing act” has been often used by Prof. Cory Budischak at Delaware Technical Community College. A more detailed analysis of a future scenario in which 99.9% of the electricity is provided by solar and wind can be found in a paper that he published a few years ago in J. Power Sources: